Method and system for directing an exchange associated with an anonymously held token on a blockchain

ABSTRACT

The invention provides a method and corresponding system for controlling the generation of a blockchain transaction, and/or the recipient of a transaction output. It can also be used to control and record the ownership of an asset represented on the blockchain without the need for a separate registry of ownership. The ownership and transfers thereof can be handled and recorded without the need for knowledge of the parties involved or their identities. According to one embodiment, the method comprises the steps of identifying at least one transaction (Tx) on a blockchain which comprises: an unspent transaction output (UTXO) relating to a tokenised asset associated with an asset controller; and an input which spends an output from a previous transaction that is locked by a redeem script hash. For each identified transaction (Tx), an incomplete blockchain transaction is generated comprising: a first output comprising a copy of the redeem script hash; and a second output which is modifiable such that only the asset controller is able to specify a recipient for the second output. The incomplete blockchain transaction is communicated to the controller of the asset. The incomplete blockchain transaction is incomplete in that it is missing a required cryptographic signature. Thus, payment of income relating to the asset can be re-directed by the controller to a destination of their choice.

This invention relates generally to distributed ledger and blockchain technology, and more particularly to the use of blockchain technology for implementing systems for the automated control of computer-executed processes. It also relates to electronic communication and notification techniques. An embodiment of the invention provides a solution for recording and controlling the ownership or control of an electronic asset via the blockchain, and for generating and effecting blockchain transactions in response to the current ownership data. The invention also provides a novel and advantageous solution for controlling and enabling the transmission of an electronic communication to a recipient. It utilises blockchain technology to facilitate the storage of a recipient address or identifier so that privacy and/or security can be enhanced, and enables the recipient to specify and/or alter the notification address stored on the blockchain. The invention is suited for, but not limited to, use with the Bitcoin blockchain.

In this document we use the term ‘blockchain’ to include all forms of electronic, computer-based distributed ledgers, including, but not limited to blockchain and transaction-chain technologies, permissioned and un-permissioned ledgers, shared ledgers and variations thereof. The most widely known application of blockchain technology is the Bitcoin ledger, although other blockchain implementations have been proposed and developed. While Bitcoin may be referred to herein for the purpose of convenience and illustration, it should be noted that the invention is not limited to use with the Bitcoin blockchain and alternative blockchain implementations and protocols fall within the scope of the present invention.

A blockchain is a consensus-based electronic ledger which is implemented as a computer-based decentralised, distributed system made up of blocks which in turn are made up of transactions. Each transaction includes at least one input and at least one output. Each block contains a hash of the previous block to that blocks become chained together to create a permanent, unalterable record of all transactions which have been written to the blockchain since its inception. Transactions contain small programs known as scripts embedded into their inputs and outputs, which specify how and by whom the outputs of the transactions can be accessed. On the Bitcoin platform, these scripts are written using a stack-based scripting language.

In order for a transaction to be written to the blockchain, it must be “validated”. Network nodes (miners) perform work to ensure that each transaction is valid, with invalid transactions rejected from the network. Software clients installed on the nodes perform this validation work on an unspent transaction (UTXO) by executing its locking and unlocking scripts. If execution of the locking and unlocking scripts evaluate to TRUE, the transaction is valid and the transaction is written to the blockchain. Thus, in order for a transaction to be written to the blockchain, it must be i) validated by the first node that receives the transaction—if the transaction is validated, the node relays it to the other nodes in the network; and ii) added to a new block built by a miner; and iii) mined, i.e. added to the public ledger of past transactions.

Although blockchain technology is most widely known for the use of cryptocurrency implementation, digital entrepreneurs have begun exploring the use of both the cryptographic security system Bitcoin is based on and the data that can be stored on the Blockchain to implement new systems. It would be highly advantageous if the blockchain could be used for automated tasks and processes which are not limited to the realm of cryptocurrency. Such solutions would be able to harness the benefits of the blockchain (e.g. a permanent, tamper proof records of events, distributed processing etc) while being more versatile in their applications.

One area of current research is the use of the blockchain for the implementation of “smart contracts”. These are computer programs designed to automate the execution of the terms of a machine-readable contract or agreement. Unlike a traditional contract which would be written in natural language, a smart contract is a machine executable program which comprises rules that can process inputs in order to produce results, which can then cause actions to be performed dependent upon those results.

Another area of blockchain-related interest is the use of ‘tokens’ (or ‘coloured coins’) to represent and transfer real-world entities via the blockchain. A potentially sensitive or secret item can be represented by the token which has no discernable meaning or value. The token thus serves as an identifier that allows the real-world item to be referenced from the blockchain.

Data relating to smart contracts needs to be registered, tracked and recorded. For example, it is necessary to record data relating to the owner(s) of an asset managed by a smart contract. This is particularly important in relation to smart contracts relating to assets which are owned by a number of entities, where the ownership is split into shares. In such cases, a transfer of ownership needs to be recorded in a secure manner. It is also important that relevant costs can be accrued against the asset and/or income generated and paid from it. Another important consideration is that it is often desirable to protect the identity of the real world parties involved.

In general, holding a tokenised asset against a blockchain means that there is a UTXO (unspent transaction output) that is allocated to the current asset holder and which determines the scale of that asset holder's current holding. This is encapsulated within the redeem script required to transfer the asset, and would generally be of the form:

-   -   X OP_CHECKMULTISIG (Metadata-A Metadata-B PublicK-A) Y

However, the information that is held within the blockchain is not this script, but rather a hash of the script. This means that the critical public key information is not available for public inspection.

In some cases, the income distribution is paid via the same tokenised commodity as the original asset e.g. when additional shares in a company are issued as the dividend. In such cases, the non-availability of the public key is not a problem as the income distribution can simply be paid to the same redeem script hash as the original issuance transaction.

However, in the more common scenario where the income distribution is paid as an alternative asset (for example BTC dividend against a share), then this lack of public key information means that, in accordance with the current state of the art, a separate, off-chain, database has to be maintained of the public keys associated with each issuance transaction. Whilst such a solution is clearly viable, it means that there are two systems (the blockchain and the off-chain database) which are maintaining the asset register. This injects complexity into the solution and the possibility that the two databases will become out of step with one another. It also requires additional storage resources.

Thus, it is desirable to provide a solution which, at least:

-   -   Facilitates or enables control, influence or direction of a         secure transfer via a blockchain to an anonymous party, such         that the     -   eliminates the requirement for this second database, and thus         the risk it entails, by enabling the automated determination of         where the transfer should be made to (e.g. where income should         be paid to)     -   is able to pay that income in such a manner that ensures that         only the current asset holder is in a position to claim those         funds     -   provides a generic mechanism to generate actions and technical         responses (e.g. in response to income generation) in proportion         to the current ownership of an asset represented and/or         referenced via a blockchain     -   uses blockchain transactions to allow the secure, automated         transfer of an asset and record those transfers and payments on         the blockchain, thus providing benefits such as a tamper-proof         record of events and data     -   enables the protection of identities of ‘real world’ parties         such as asset owners; the solution should enable or facilitate         anonymity     -   provides a solution for enabling and controlling electronic         communications which need to be sent to “unknown” parties.

Such an improved solution has now been devised. The present invention provides at least these technical effects discussed above.

The invention is defined in the appended claims. Therefore, in accordance with the invention there may be provided a control method and corresponding system.

The method may be a method of controlling the transfer of an entity or item, or part thereof. It may be transferred electronically, preferably via a blockchain. The entity or item may be referred to for convenience herein as an asset, or part of an asset, and may be represented, tokenised and/or referenced on or via the blockchain. Additionally or alternatively, it may be a method of controlling the generation of a blockchain transaction. It may provide an automated solution—which does not require human intervention for its operation.

Additionally or alternatively, it may be described as a method of controlling and/or specifying the recipient of a blockchain transaction output. It may be described as a method of controlling, directing and/or influencing a transfer via a blockchain. The transfer may relate to an asset or a portion of cryptocurrency or funds and/or some other resource via a blockchain. It may be a transfer of control of such an item from the output of one transaction to the input of another. It may be a method of re-directing such a transfer.

The blockchain transaction may be related or associated with an asset represented on the blockchain. The asset may be a tokenised asset. The asset may be associated with a (smart) contract.

The method may comprise the step of:

-   -   identifying at least one transaction (Tx) on a blockchain which         comprises:         -   an unspent transaction output (UTXO) relating to a tokenised             asset associated with an asset controller; and         -   an input which spends an output from a previous transaction             that is locked by a redeem script hash.

The method may comprise the step of:

-   -   for each identified transaction (Tx), generating an incomplete         blockchain transaction comprising:         -   a first output comprising a copy of the redeem script hash;             and         -   a second output which is modifiable such that only the asset             controller is able to specify a recipient for the second             output.

The controller of the asset may be an owner or some other entity associated with the asset. The asset controller may be a computing resource that is representative of a real world controller or owner. The computing resource may be an automated agent. The asset may be represented on the blockchain as a token (or “coloured coin”) provided within the metadata of a transaction script.

The recipient may be specified using a cryptographic key.

The blockchain may be the Bitcoin blockchain, or an alternative implementation of an electronic distributed ledger.

The method may further comprise the step of:

sending the incomplete blockchain transaction to the controller of the asset.

The incomplete blockchain transaction may be incomplete in that it is missing a required cryptographic signature.

The incomplete transaction may further comprise:

-   -   an input which spends the unspent transaction output (UTXO);         and/or     -   an input which spends an output of another transaction so as to         transfer an amount of value or currency to the asset controller.

The method may comprise the step of:

modifying the second output of the incomplete transaction so as to include a cryptographic signature. The modification step may be performed by the Asset controller.

The step of identifying the at least one transaction (Tx) may involve or comprise traversing the blockchain to arrive at a blockchain transaction which comprises an unspent output (UTXO) relating to the asset.

At least one step of the method may be performed by an autonomous computing agent.

The method may further comprise the step of:

Completing and/or modifying the incomplete transaction by specifying a recipient for the second output. Additionally or alternatively, it may comprise the step of submitting the completed transaction to the blockchain.

The incomplete transaction may be arranged such that the output(s) can be modified. The incomplete transaction may comprise a signature type which requires that all inputs are signed but none of the outputs. The signature type may be the Bitcoin SIGHASH_NONE signature type or a substantially functional equivalent thereof in another blockchain protocol, such that the signature type facilitates or enables modification of transaction output(s).

The method may further comprise the step of:

spending the unspent transaction output (UTXO) to transfer the tokenised asset to a recipient address.

The method may further comprise the step of:

spending the output of the previous transaction to transfer or re-issue ownership of the asset.

The amount of cryptocurrency associated with the second output may be calculated by a computing resource in accordance with rules provided in a smart contract.

The second output of the incomplete transaction, when spent, may transfer an amount of currency or value to a recipient. This currency or value may be any type of resource. It may, for example, be an amount of cryptocurrency or some tokenised funds or other commodity.

The invention also provides a corresponding system. The system may be arranged to perform the steps of any preceding claim.

The system may comprise:

a blockchain;

at least one autonomous computing agent arranged and configured to:

traverse the blockchain; and/or

generate the incomplete transaction; and/or

send the incomplete transaction to a recipient.

Additionally or alternatively, the invention may comprise a pone or more steps arranged to control, direct or influence the transmission of an electronic communication. Thus, the method of the invention may be described as a method of establishing an electronic communication channel between two or more parties.

Additionally or alternatively, the invention may be arranged to facilitate and/or enable the completion of an incomplete blockchain transaction. Thus, the invention may be described as a method to control or influence the validity and/or propagation of a blockchain transaction on a blockchain network.

Herein, the terms “communication”, “notification” and “alert” may be used interchangeably.

Thus, the invention may provide a method of controlling and/or generating an electronic communication. Additionally or alternatively, the invention may provide a solution for determining the destination or recipient of an electronic communication/transmission. It may be a blockchain-implemented solution. The invention may be a method/system arranged to enable (electronic, off-blockchain) communication with an anonymous recipient, or pseudo-anonymous recipient. This recipient may be an asset owner or controller, for example, although the invention is not limited in this regard. The communication may be sent using information stored, or “embedded”, within a sequence of blockchain transactions. The invention may be described as a method of specifying and/or determining the destination of an electronic communication via a blockchain.

The method may comprise the step: sending a signal to an address. The address may be a notification address. The signal may be called or serve as an (electronic) notification or communication.

The invention is not limited with regard to the context, purpose or content of the notification.

The notification may be provided as metadata within an unlocking script associated with an input of a transaction (Tx₁) on a blockchain. The term “identifier” may be used interchangeably with “address”. This transmission step may triggered by an event. The event may be specified, determined or influenced by a smart contract. Transmission (sending) of the notification may be performed by a computer-based resource. It may be performed as at least part of an automated process.

The notification may serve as a request and/or trigger for completion of the incomplete transaction. The method may comprise the step of completing the incomplete transaction. Completion may comprise the provision of a cryptographic signature.

The unlocking script may be provided in order to spend an output from a further transaction (Tx₂) on the blockchain. (This may be a “preceding” transaction on the blockchain in the sense that an input of transaction Tx₁ may spend an output of transaction Tx₂).

Thus, the invention may comprise the step of requiring the provision of a notification address in an unlocking script in order to unlock a locking script. This step may be repeated. Thus, a sequence of notification addresses may be required and supplied. A notification address may be required in order to spend each output in a chain of blockchain transactions. This allows the provision of a different addresses over time. Thus, the invention enables and facilitates changing of the recipient address for the notification.

The input of the transaction (Tx₁) and/or the output of the further transaction (Tx₂) may be associated with a tokenised asset represented on, or referenced via, the blockchain. This token may be referred to as a “coloured coin”.

The electronic notification may comprise:

-   -   an incomplete or complete blockchain transaction, and/or     -   information relating to an incomplete or complete blockchain         transaction.

It may be incomplete in the sense that it is missing a piece of required data.

It may comprise information relating to the location of the complete/incomplete transaction, or how to access it.

The notification address may be associated with an asset or resource represented on the blockchain, or a controller of an asset or resource represented on the blockchain. The controller may be the same or a different entity from the actual (“real world”) owner of the asset.

The method may further comprise the step of:

traversing the blockchain to identify the transaction (Tx₁) or further transaction (Tx₂). The skilled person would understand how this traversal would be performed as per known techniques.

The method may comprise the step of:

submitting a transaction to a blockchain, wherein the transaction (TO comprises an unspent output (UTXO) which includes a redeem script that requires the provision of a notification address within the metadata of an unlocking script in order to spend the output (UTXO).

The unspent output (UTXO) may transfer ownership of, or otherwise relate to, a tokenised asset represented on, or referenced via, the blockchain.

The notification address may be provided as a parameter in the unlocking script of the transaction (Tx₁). It may be provided as a second parameter.

The method may comprise the step of using a redeem script to ensure that a notification address has been provided in the unlocking script. The redeem script may comprise a value indicating how many notification addresses must be supplied by the unlocking script.

A plurality of notification addresses may be provided within the unlocking script.

The notification address may be a network address, a cryptographic key, a uniform resource locator (URI), email address or any other address or identifier which can be represented in the metadata of a script and used as a destination for an electronic communication. Thus, the notification address may serve as an identifier for the recipient of the notification/communication.

At least one step of the method may be performed by an automated computing resource or agent. This may be called a “bot” or “oracle”.

The method and/or system may be substantially as described below in the section entitled “Notification Address Embedded Within the Blockchain”.

The invention may also provide a computer-implemented system arranged and configured to perform the steps of any embodiment of the method described herein.

The system may comprise:

a blockchain;

at least one autonomous computing agent arranged and configured to:

traverse the blockchain; and/or

generate and or send the electronic notification.

Any feature described in relation to the method may also be applicable to the system and vice versa. Any feature described above in respect of one embodiment or aspect may be present in any other embodiment or aspect of the invention.

The invention may be substantially as described in the illustrative embodiment described in the following examples, description and figures. These and other aspects of the present invention will be apparent from and elucidated with reference to, the embodiment described herein.

An embodiment of the present invention will now be described, by way of example only, and with reference to the accompany drawings, in which:

FIG. 1 provides an overview of an illustrative embodiment of the invention.

FIG. 2 provides an illustration of the traversal logic which is employed when iterating over the blockchain to determine the current ownership of the asset(s).

FIG. 3 provides an illustration of the transaction output which is required in accordance with an embodiment of the invention.

FIG. 4 provides an illustration of the construction of the initial, incomplete blockchain transaction.

FIG. 5 provides an illustration of the incomplete transaction of FIG. 4 after it has been amended and completed by the asset controller.

FIG. 6 provides an illustration of an embodiment of the invention, in which a notification is sent to the asset controller to inform them that there is an incomplete transaction which needs their attention and modification.

FIG. 7 shows an illustration of a use case model in accordance with an embodiment of the invention.

FIG. 8 provides blockchain transaction number 100.10 which, in relation to the example provided below, could be used to generate shares in the asset represented on the blockchain.

FIG. 9 provides blockchain transaction number 100.120 which, in relation to the example provided below, could be used to issue shares of the asset to a recipient. Note that the notification address is specified as a requirement in the ScriptSig. This forces the recipient (i.e. the asset owner or controller) to provide a notification address as metadata in an unlocking script when “claiming” the shares via an input in a subsequent transaction.

FIG. 10 provides blockchain transaction number 150.10 which could be used to transfer ownership of part of the asset to a recipient. In this case, the current asset controller retains part of the asset and assigns or transfers the other portion to one or more other parties.

FIG. 11 provides incomplete blockchain transaction number 400.1 which could be generated in relation to the example provided below.

FIG. 12 provides blockchain transaction number 400.10 which is the completed version of the incomplete transaction shown in FIG. 11 , as modified by the asset controller.

The present invention provides a generic solution that allows the control of secure transfers of digital entities via inputs and outputs of blockchain transactions. In the examples provided herein, the invention is discussed for illustrative purposes only in the context of paying income or accrued costs against a blockchain-registered asset according to the terms of an underlying investment contract e.g. in direct proportion to how the ownership of that asset has been split. For example, if an asset has been split into 100 shares, then the income to be paid would be calculated per share.

However, it is important to note that the invention is not limited to such use case scenarios and provides a more generic transfer-control solution and notification solution which can be utilised to advantage in a variety of applications and contexts.

Key Terms

This technical specification uses the following terms throughout to define key concepts and components.

Name Type Asset The asset is an actor that represents something that can apportion ownership to one of more Asset holders in variable amounts. The Asset is both a private key plus an agent as defined below. These amounts can be simple percentages (e.g. 5%) or units (e.g. 100 units). Agent/oracle The ‘agent’ is a software-implemented resource which performs automated actions on behalf of the asset. The agent may be referred to as an “oracle” or a “bot”. Essentially, the agent is a software component which is programmed to implement the terms of the smart contract, respond appropriately to pre-defined triggers, evaluate conditions using inputs from sources which may be off-chain etc. As such agents are known in the art and readily understood by the skilled person, and are not the focus of the present invention, their implementation are not described in detail herein. Asset Holder The asset holder is an actor that represents something that currently holds a proportion of an Asset. The holder may be referred to as a “controller” or “owner” Secondary The secondary asset holder is an actor that represents Asset Holder something that holds a proportion of an Asset which is gained from a transaction other than the original issuance transaction (e.g. the on-sell of the asset). Repository The repository is an actor that represents the entity responsible for the storage (and potentially on-going maintenance) of the Contract document defining the payment schedule associated with the asset. Contract The Contract is the document that contains the formal definition for how to determine the payments, and the schedule associated with the payments for this asset. This is a smart contract, as is known in the art. It may also (depending on the implementation method used) hold detailed of the current ownership of the asset.

As shown herein, the invention provides an automated, secure and robust mechanism which allows at least the following:

-   -   the ability to determine the current ownership of an asset from         a blockchain (such as, for example, the Bitcoin blockchain);     -   the ability to control transmission of electronic communications         to unknown parties relevant to the asset; and     -   the ability to pay income generated by the asset in proportion         to the current ownership of the asset.

In the latter two cases, this process can used to advantage where the asset maintains a separate database of ownership, or where the ownership is hidden by the blockchain via the use of (payment) addresses.

The invention provides at least two advantageous aspects:

-   -   1. The ability to make payments via a blockchain to owners of an         asset where the owner remains unknown and anonymous to the         asset;     -   2. The ability to notify anonymous owners using information         stored within a sequence of blockchain transactions.

Determining Current Ownership of an Asset Represented on a Blockchain

In order to apportion costs/income against an asset represented on the blockchain, it is essential to be able to determine the current ownership of that asset. There are two mechanisms one could use to achieve this:

-   -   The ownership can be maintained in a separate register off-chain         maintained by the asset (and updated by forcing transfers to be         counter-signed by the asset). This mechanism is ideal for         regulated assets where formal “Know Your Customer” rules apply.     -   The ownership can be determined by scanning the transactions on         the blockchain to dynamically generate the current ownership         list. It should be noted that this approach does not determine         the ownership per se but rather it identifies the Bitcoin         addresses that are responsible for the asset. This may be         referred to as the “asset controller”, which may or may not be         the actual owner. This blockchain-traversal technique is used by         the present invention.

Generating Ownership-Related Actions: E.g. Calculating and Paying Income

In order to pay income from the asset in proportion to the current ownership of the asset:

-   -   the asset must have the ability to determine the current         ownership;     -   the asset must be able to record the total income for a given         period;     -   the asset must be capable of dividing the income between the         current ownership;     -   the asset must be capable of netting costs from the income;     -   the asset must be capable of holding income where previous costs         have not been paid; and     -   the asset must be capable of triggering the payment of the         income such to the current asset holders.

This income can be rolled up at the end of a time-period (e.g. every six months) or as it is generated (e.g. immediately). Depending on the nature of the contract, the same conditions would allow for pro-rata payment of income with some contracts only allowing payment for a period to the current holder.

Technical Solution

The technical solution provided by the invention provides a mechanism by which the controller of an investment or asset, via an agent and a smart contract, can generate a set of payment transactions to both re-coup its costs or pay income. The solution relies on an automated oracle process (or multiple oracle processes depending on the structure of the underlying contract) being triggered by an off-chain condition. For example, this condition might be a date on which to pay returns. Once this trigger condition trips the oracle will:

-   -   calculate the total payment amount for the asset as a whole;     -   calculate the individual payments across the current ownership         split for the asset based on the payment rules (for example,         pro-rata); and     -   create payment transactions for each of the individual asset         holders.

FIG. 1 shows the basic flow of how the technical solution determines the individual payments to make.

The steps in the flowchart of FIG. 1 are defined in more detail in the subsequent sections:

Step Details 1 Find ‘anchor’ transaction This specifies to the oracle the point to start the traversal of the transaction history to determine the current ownership of the assets. The anchor may also be referred to as the “issuance transaction” See section ‘Traversing from the issuance transaction’ for more information. 2 Traverse transaction history to determine current UTXO set This looks for all the “spends” of the assets, starting from the point of issuance, to determine the current unspent output UTXO (which determines the current location/ownership of the assets). See section ‘Traversing from the issuance transaction’ for more information. 3 For each UTXO, create distribution transaction This step simply ensures that steps 3 through 6 are repeated for each UTXO discovered in step 2 above. A ‘raw’ distribution transaction is created and broadcast in an incomplete state (it is missing a key transaction signature). The distribution transaction will ultimately be used to transfer funds to the specified recipient, once the distribution transaction has been completed. See section ‘Creating the distribution payment’ for more information. 4 Broadcast distribution transaction This steps broadcasts the incomplete transaction to interested parties. Since it is known that only the current controller/owner of the asset can complete the transaction and claim the funds (because of the requirements specified in the locking script of the output), this can be published through any open channel. However, it cannot be broadcast through the blockchain itself, for technical reasons explained below. 5 Asset owner re-directs distribution to their select key This step allows the current asset controller/owner to re-direct the funds from the broadcast transaction to their selected private key. See section ‘Re-directing the distribution payments’ for more details. 6 Distribution transaction published to the blockchain This final step locks the completed and re-directed transaction to the blockchain in the normal manner.

Traversing the Blockchain from the Issuance Transaction

In order to determine the current location (ownership) of the shares within the asset, the relevant oracle needs to be able to traverse the blockchain, starting from the original issuance transaction to determine where the shares of the current asset currently reside. The issuance transaction is referred to as the “anchor transaction” in FIG. 1 .

FIG. 2 shows a sample chain of transactions which might be used during such a traversal. Essentially, this process involves moving from transaction to transaction on the blockchain, following a trail, until the oracle finds a UTXO relating to the asset. As this output has not been spent, it indicates that the asset controller that spent the last input on the asset must still be the controller. Therefore, the traversal process can halt at this transaction.

Each individual Issue or Transfer transaction output has an associated Redeem Script. From the fact that the transaction output is unspent, the oracle can determine which Redeem Script was used to spend the output from the previous transaction and therefore ‘owns’ which proportion of the asset at any point in time.

Creating the Distribution Payments

By knowing the redeem script, the income distribution transaction can make use of the SIGHASH_NONE capability to allow the output to be redirected, but only in a manner that the controller of the Redeem Script can change. To do this, the distribution transaction needs to be constructed as illustrated in FIG. 3 .

The distribution transaction will have two outputs:

-   -   1. an output which transfers (re-issues) back to the current         controller so that next time the traversal process is performed,         the same controller is determined to be the current one; and     -   2. an output which transfers some electronic funds to the         controller.

The re-issuance output can be constructed since it can simply replay (i.e. copy) the Redeem Script hash from the previous issuance/transfer transaction.

However, it is impossible to construct the distribution transaction in one step based on the number of signatures that are required and because, at the point of construction, the locking script for the Income Payment to A cannot be constructed.

To solve this, the distribution transaction is originally constructed and broadcast in the format shown in FIG. 4 .

By setting the signature hash on the inputs to SIGHASH_NONE, then either one of the outputs can be changed. (Note: one or more embodiments of the invention may be implemented on a protocol other than the bitcoin protocol. The important point is that the outputs are set up such that they can be modified). However, by locking in the last issuance transaction, only the legitimate owner of the asset can make the change since they are required to sign the input (and would obviously not do so unless it was in their interests). It should be noted that there is no necessity for any signature to be supplied on the Last Asset Issue/Transfer to A Transaction. It is shown in FIG. 4 on the assumption that the asset issuer is a counter-signatory for any transfer transaction; if they are not then this transaction is simply bound using the signature on the Income for Distribution which achieves the same effect.

Re-Directing the Distribution Payments

When the current Asset owner picks up the incomplete, template transaction, they determine that it is in their best interests to complete the transaction which they do by signing the Last Asset Issue/Transfer to A Transaction input after changing the income payment transaction to pay this income to themselves. This amended, complete transaction is illustrated in FIG. 5 . As the transaction is now complete it can be mined.

Thus, the outcome has been achieved without there being any requirement for the Asset to know anything about the underlying owner of the asset other than their ownership share that was contained within the blockchain record itself.

The Need for Notification

As described above, the payment distribution transaction is initially created in an incomplete form. It then needs to be communicated somehow to the asset controller(s) so that they are aware of its existence and can make the necessary modifications to complete it and submit it to the blockchain.

However, the incomplete transaction cannot be broadcast via the blockchain itself. This is because, by default, the blockchain propagation nodes will not propagate incomplete transactions across the network. As the original version of the distribution transaction is incomplete (it is missing a signature), it is unlikely that the controller/owner will be able to pick up the incomplete transaction and apply a signature prior to it being dropped by the network. Whilst this does not impact the ownership of the asset, it does mean that the relevant parties do not get paid the income that they are owed.

Thus, there is a technical problem that needs to be overcome, namely how to communicate an incomplete blockchain transaction (Tx) (or its presence) to a recipient in cases where the recipient's identity and/or other information is unknown. To resolve this technical problem, there needs to be a channel that can be used to broadcast the incomplete transaction to interested parties or at least make them aware of its existence and/or location.

There are various possible methods to resolve this, including:

-   -   The contract could publish a ‘broadcast’ channel as part of the         contract upon which all incomplete transactions will be         broadcast with owners of the assets listening to that channel to         determine transactions of interest and reacting to them. This         publish/subscribe mechanism is a standard IT feature.     -   Upon sale or other transfer of the asset, the new asset         owner/controller locks a notification address into the sale         transaction. This enables a communication channel to be set up         without any other information being known about the asset         owner/controller. The asset will then use this private channel         to send the incomplete transaction to the current owner, or         notify them that the transaction is available from an accessible         location e.g. for download and subsequent completion.

Neither of these solutions impact or affect the first aspect of the invention as described above, in that the asset is still unaware of the ownership of itself other than from information held upon the blockchain itself. In the following example, the transactions make use of the second option for transaction notification. This notification technique forms a second, novel aspect of the invention and offers privacy or anonymity of the transaction information.

Notification Address Embedded within the Blockchain

This aspect of the invention provides a solution to the propagation problem identified above by enabling the ability to embed a notification address within the blockchain transaction. The notification address can then be used for subsequent notifications. This section explains how this model operates.

The notification can take any suitable form, such as for example an email. In such cases, the email would be sent to the email address that has been embedded in the previous transaction. However, other forms of electronic communications known in the art also fall within the scope of the invention. Essentially, the identifier which is captured in the initial transaction serves as the address or location to which notifications will be sent.

It should be noted that this notification technique can be used to advantage as a solution to a problem in its own right, and in respect of a wide variety of contexts and applications, independently from the first aspect of the invention described above.

In the present example, though, the role of the notification address is to ensure that the relevant interested actors can be notified to apply their signatures (and make other amendments) to a given target transaction as the author of that target transaction has no other information about them.

This solution means that a communication can be sent to a recipient without the need for any further information to be supplied or known. The invention therefore provides an enhanced alert, notification or communication technique which preserves or enhances privacy and security. No additional information about the recipient is required other than the address that is provided in, and then extracted from, the transaction script. This lends itself to being implemented by an automated process such as a bot.

Transmission of the notification to the specified address may be triggered by an event. The event may be specified in, or influenced by, a smart contract.

The notification can simply be a signal sent to the address, and/or may contain predetermined content. Thus, a desired, informative message can be transmitted. Additionally or alternatively, receipt of the notification may serve as a signal to an automated process and thus trigger a predetermined or programmed response e.g. to supply a signature to the transaction, or perform some other action.

The invention is not limited with regard to the content of the notification message that is dispatched to the embedded address. The notification may, in some cases, include a copy of the incomplete transaction. In the present example, though, the role of the notification address is to ensure that the relevant interested actors—which may be a human or computer-based resource—can be notified or alerted to the need to apply their signatures (and make other amendments) to a given target transaction as the author of that target transaction has no other information about them. In effect, then, the invention enables the fulfilment, completion of a future blockchain transaction. Upon provision of the necessary signature(s), the partial, invalid transaction is converted into a viable, valid transaction that can be accepted by the blockchain. Therefore, the invention solves the problem of how to control, facilitate and/or enable the validity of a blockchain transaction and its propagation on a blockchain network.

In order to do this, a ‘seed’ transaction needs to be created that forces the capture of notification address in all subsequent transactions. This would usually be prior to an issuance transaction (for a standard tokenised transaction). This issuance or ‘source’ transaction now requires additional attributes to be supplied on the unlocking script that contain the notification addresses. The full flow of this process is shown in FIG. 6 .

Notification Redeem Script

The key format for the unlocking script is as follows:

-   -   <count of notification addresses>     -   <notification address #1>     -   <notification address #2>     -   . . .     -   <notification address #n>

  <signature #1> . . . <signature #n>

As can be seen from the above structure, the elements shown in the box represent a standard script input, but the prefix is novel. This prefix takes the form shown here:

OP_DUP OP_IF OP_1SUB OP_SWAP OP_DROP OP_DUP OP_ENDIF OP_IF OP_1SUB OP_SWAP OP_DROP OP_DUP OP_ENDIF OP_IF OP_1SUB OP_SWAP OP_DROP OP_DUP OP_ENDIF OP_IF OP_1SUB OP_SWAP OP_DROP OP_ENDIF OP_VERIFY <Script remainder e.g. signature verification>

This particular example means that the <Count of notification addresses> can range from 1 to 4, but the structure can be extended to support a different maximum if required. This script prefix effectively drops the relevant notification addresses from the stack, and then checks to make sure that the number of notification addresses matches the number that should have been there.

Use Case Model

The model provided in FIG. 7 shows the key use cases involved within the non-debt lending model.

Issuance of Shares

The Asset needs to issue shares in itself to the appropriate Asset Holder, ensuring that it captures the notification address for that entity during the issuance. The primary actor in this is the Asset.

Main success scenario:

This step is required only where the current holder's notification details are maintained on the blockchain itself.

Step Details 100.10 Shares Generated In this step, the Asset splits their stock of BTC into UTXO's of the correct amount for subsequent issuance to an individual Asset Holder (the step performed in 100.20 below). The transaction is made to a pay to script hash address controlled by the Asset but which allows the injection in step 100.20 of the new Asset Holder's notification address. 100.20 Shares Issued In this step, the Asset takes each individual fragment generated in step 100.10 above and issues it to the appropriate Asset Holder locking that holder's notification address into the issuance instruction within a second parameter to the unlocking script.

The Share Generation transaction is shown in FIG. 8 as Transaction 100.10

The full redeem script for Output 1 of transaction 100.10 is shown below.

-   -   OP_DROP OP_CHECKSIG

The Share Issuance transaction is shown in FIG. 9 as Transaction 100.20

The full redeem script for Output 1 of transaction 100.20 is shown below.

OP_DUP OP_IF OP_1SUB OP_SWAP OP_DROP OP_DUP OP_ENDIF OP_IF OP_1SUB OP_SWAP OP_DROP OP_DUP OP_ENDIF OP_IF OP_1SUB OP_SWAP OP_DROP OP_DUP OP_ENDIF OP_IF OP_1SUB OP_SWAP OP_DROP OP_ENDIF OP_VERIFY OP_CHECKMULTISIG OP_2 <PubK-AssetHolder> <PubK-Asset> OP_2

This example redeem script allows a subsequent on-sell to transfer ownership to up to four buyers. If the purchase relates to more than four buyers, then multiple transactions would be required. It should be noted that it is clearly possible to extend (or restrict) the potential number of new purchasers by repeating (or reducing) the ‘if’ block within the above script.

On-Sell of Shares

The Asset Holder needs to on-sell a proportion of its holdings to another interested party. The primary actor in this is the Asset Holder.

Main success scenario:

Step Details 150.10 Capture notification address for each purchaser The current asset holder captures the notification address for the new purchaser through any mechanism that they choose. 150.20 Create re-sell transaction template The current asset holder constructs a re-sell transaction and captures the order of the transaction outputs. The order of the created transaction outputs is used to structure the unlocking script as follows: <Number of transaction outputs> <Notification Address for TxOut-0> <Notification Address for TxOut-1>  // if required <Notification Address for TxOut-2>  // if required <Notification Address for TxOut-3>  // if required <Sig-AssetHolder> 150.30 Asset counter-signs template transaction The Asset provides the second signature to the re-issuance transaction. 150.40 Transaction published & mined The transaction is then published to the blockchain and subsequently mined into a block.

This creates a number of key features that are necessary to support the underlying income distribution.

-   -   The sale can only be to a maximum of four new holders (e.g. a         four output transaction, but can be any number from 1 to 4).     -   If the sale includes the retention of some of the shares, then         only three new holders can be supported since only of the slots         is taken for the re-allocation back to the current holder

Transaction 150.10

In example transaction 150.10 provided in FIG. 10 , the transaction implements a partial sell with the current asset holder retaining a stake and selling one other stake to a new holder. It should be noted that in a real-world scenario it is possible that an additional input to cover the mining fee may be required. This has been ignored in the template of FIG. 10 , transaction 150.10 to improve readability.

The redeem script for output 1 of transaction 150.10 (FIG. 10 ) is the same as that for transaction 100.20 (FIG. 9 ) with the exception that the public keys are: <PubK-SecondaryAssetHolder> and <PubK-Asset>.

This redeem script for output 2 of transaction 150.10 (FIG. 10 ) is completely identical as that for transaction 100.20 (FIG. 9 ).

Determination of Ownership

The Asset needs to determine how to allocate the income for payment to the current asset holders even though it is unaware of their identity. The primary actor in this action is the Asset.

Main success scenario:

Step Details 200.10 Determine Current Asset Allocation In this step, the Asset traverses the pool of UTXOs from their original issuance transaction generated by the asset. Where the original UXTO has been spent (i.e. the asset has been transferred again), then the outputs from this new transaction is checked according to step 200.10. In performing this traversal, the notification address from the ‘spent’ input is recorded. Each original issuance UTXO is traversed until a set of current issuance blocks is determined, plus the notification address and redeem script for that output.

Calculate Payment

Here, the Asset wishes to calculate the amount of income that should be paid to its current owners. The primary actor for this action is the Asset.

Main success scenario:

Step Details 300.10 The Asset pulls in all the information for the period to calculate the income due. Note: this may be zero. Note: the mechanism used will be specific to the nature of the asset itself and formally defined within the associated contract document. 300.20 The outputs from the preceding step is allocated on a per share basis according to the terms of the contract (for example by dividing the output value with the number of shares in existence). The rounding rules will tend to be defined within the associated contract document but will normally be down for income due. 300.30 The per-unit apportionment derived in step 300.20 is now allocated on a per-holding basis through a simple multiplication using the holding allocation derived in use case 200. 300.40 Use case 400 is now performed for each individual holding identified out of step 300.30

Paving the Income

Here, the Asset wishes to pay income to its owners in proportion to their ownership. The primary actor is the Asset.

Main success scenario:

Step Details 400.10 The Asset generates a transaction with two transaction inputs and two transaction outputs as shown in FIG. 4. The transaction inputs are:   Asset issuance transaction (or last asset re-assignment),   signed by the Asset with a SIGHASH_NONE flag set   Income distribution amount, signed by the Asset with a   SIGHASH_NONE flag set This means that there is a signature missing from the first input and allows anyone to change the outputs of this transaction. However, because of the missing signature, this is effectively changed to a model that says that only the remaining signatory has the practical ability to change the output of the transaction. In turn, this has allowed the Asset to create a payment transaction without knowing where to send the payment, but certain that it will only get collected by the authorised recipient. The transaction outputs are:   Transaction income distribution input (less the mining   fee) paid to the Asset's public key hash   Asset issuance transaction, paid back to the same place   as the input. 400.20 Using the notification address for this redeem script (as determined during use case 200), the incomplete transaction is pushed to the current Asset Holder. 400.30 Upon receipt, the Asset Holder changes the destination of the second output to the Asset Holder's public key hash (e.g. paid to themselves) and then provides the second signature to the asset issuance transaction with a standard SIGHASH_ALL flag set. Note that the re-direction of the income distribution output can be to any address that the Asset Holder requires and is not restricted to being their public key hash. 400.40 The Asset Holder then publishes this transaction to the blockchain for it to be accepted and mined.

Transaction 400.10—Interim (Incomplete) transaction is shown in FIG. 11 . Transaction 400.10—final (complete transaction) is shown in FIG. 12 . In FIG. 12 , the amendments are shown in bold for clarity.

Example Scenario: Asset Share Capital

The main type of scenario that is supported by this model is the traditional share capital for an asset such as a company. The company (NewCo plc) will issue a fixed amount of shares (1,000) that can be freely traded, with income paid out on a periodic basis (annually). As the income distribution represents the profit of the company, there is no requirement to support the collection of costs from the asset holder base (profit has already had the costs netted off from them).

Key Benefits of the Invention Include:

The invention enables autonomous activity against a blockchain, allowing for entities that are created where income/costs can be paid without having to maintain (except for regulatory reasons) a separate off-chain database of ownership.

The invention enables a notification address or identifier to be embedded within a transaction, and specifically within the script of a transaction.

Thus, the invention provides enhanced privacy, security and communication. It is particularly advantageous in applications relating to the control and recordal of a transfer of assets and/or funds via a blockchain.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word “comprising” and “comprises”, and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. In the present specification, “comprises” means “includes or consists of” and “comprising” means “including or consisting of”. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 

The invention claimed is:
 1. A method of controlling a transfer via a blockchain, the method performed by an autonomous computing agent and comprising: identifying at least one transaction (Tx) on the blockchain, wherein the at least one transaction (Tx) comprises: an unspent transaction output (UTXO) relating to a tokenised asset associated with an asset controller; and an input that spends an output of a previous transaction that is locked by a redeem script hash; for each identified transaction (Tx), generating an incomplete blockchain transaction comprising: a first output comprising a copy of the redeem script hash; and a second output that is modifiable, only by the asset controller, to specify a recipient for the second output, wherein the second output of the incomplete blockchain transaction, when spent, transfers an amount of value or currency to the recipient; and notifying the asset controller, at a notification address of the asset controller, of the incomplete blockchain transaction, wherein the notifying comprises sending a signal and/or an electronic notification to the notification address that is provided as metadata within an unlocking script of an input of a transaction (Tx₁) on the blockchain, and wherein the signal and/or the electronic notification provides a prompt, a trigger, or an alert to the asset controller relating to the incomplete blockchain transaction.
 2. The method according to claim 1, further comprising: sending the incomplete blockchain transaction to the asset controller.
 3. The method according to claim 1, wherein: the incomplete blockchain transaction is incomplete in that it is missing a required cryptographic signature.
 4. The method according to claim 1, wherein: the incomplete blockchain transaction further comprises: an input that spends the unspent transaction output (UTXO); and/or an input that spends an output of another transaction so as to transfer the amount of value or currency to the asset controller.
 5. The method according to claim 1, further comprising: modifying the second output of the incomplete blockchain transaction so as to include a cryptographic signature.
 6. The method according to claim 1, wherein: identifying the at least one transaction (Tx) involves traversing the blockchain to arrive at a blockchain transaction that comprises the unspent transaction output (UTXO) relating to the tokenized asset.
 7. The method according to claim 1, further comprising: completing the incomplete blockchain transaction by specifying the recipient for the second output to result in a completed transaction, and submitting the completed transaction to the blockchain.
 8. The method according to claim 7, wherein: the recipient is specified using a cryptographic key.
 9. The method according to claim 1, wherein: the tokenized asset is represented on the blockchain as a token provided within metadata in a script.
 10. The method according to claim 1, wherein: the incomplete blockchain transaction comprises a signature type that requires that all inputs are signed but none of the outputs are signed, wherein the signature type is the Bitcoin SIGHASH_NONE signature type or a functionally equivalent signature type from an alternative blockchain protocol.
 11. The method according to claim 1, further comprising: spending the unspent transaction output (UTXO) to transfer the tokenised asset to a recipient address.
 12. The method according to claim 1, further comprising: spending the output of the previous transaction to transfer or re-issue ownership of the tokenized asset.
 13. The method according to claim 1, wherein: an amount of cryptocurrency associated with the second output is calculated by a computing resource in accordance with one or more rules provided in a smart contract.
 14. The method according to claim 1, further comprising: in response to the signal and/or the electronic notification, modifying the incomplete blockchain transaction, wherein modification comprises providing at least one cryptographic signature.
 15. The method according to claim 1, wherein: the signal and/or the electronic notification comprises: the incomplete blockchain transaction, and/or information relating to a location of, or means of access to, the incomplete blockchain transaction; and/or information relating to the incomplete blockchain transaction.
 16. A computer-implemented system, comprising: an autonomous computing agent performing as a node on a blockchain, the autonomous computing agent comprising: at least one processor; and memory comprising computer-executable instructions that, as a result of execution by the at least one processor, cause the autonomous computing agent to: traverse the blockchain to identify at least one transaction (Tx) on the blockchain, wherein the at least one transaction (Tx) comprises: an unspent transaction output (UTXO) relating to a tokenised asset associated with an asset controller; and an input that spends an output of a previous transaction that is locked by a redeem script hash; for each identified transaction (Tx), generate an incomplete blockchain transaction comprising: a first output comprising a copy of the redeem script hash; and a second output that is modifiable, only by the asset controller, to specify a recipient for the second output, wherein the second output of the incomplete blockchain transaction, when spent, transfers an amount of value or currency to the recipient; and notify the asset controller, at a notification address of the asset controller, of the incomplete blockchain transaction, wherein to notify the asset controller comprises a step to: send a signal and/or an electronic notification to the notification address that is provided as metadata within an unlocking script of an input of a transaction (Tx₁) on the blockchain, wherein the signal and/or the electronic notification provides a prompt, a trigger, or an alert to the asset controller relating to the incomplete blockchain transaction.
 17. The computer-implemented system according to claim 16, wherein the memory comprises additional computer-executable instructions that, as a result of being executed by the at least one processor, further cause the autonomous computing agent to: send the incomplete blockchain transaction to the asset controller. 